A decade ago, Vernon ran his Tulare County farm without the help of illegal immigrants. He had plenty of legal workers to keep the packing shed humming, irrigate and harvest the 200 acres of peaches, plums and apricots, and tend to the stuffy, smelly chicken houses.

Today, two-thirds of Vernon's 100-plus seasonal workers are illegal immigrants. He's spent the last several years brushing up on his Spanish, learning one new word a day so he can communicate with his workers.

So what's changed? Vernon -- who agreed to talk openly only if identified by his first name -- blames the government: Restrictive immigration policies make it almost impossible for low-skilled immigrants to come here legally.

He said that amnesty for illegal immigrants a quarter-century ago gave farmers in the Central Valley plenty of legal workers. But they eventually got too old for field labor or moved on to better-paying jobs, such as construction work.

"I don't like illegal immigration, and I don't think we should have it," Vernon said on a sunny afternoon in the backyard of his ranch house. "But the government doesn't provide [an adequate] way for workers to come here legally, so it's just kind of a don't-ask, don't-tell thing."

Vernon's frustration illustrates a key point: Immigrants who want to come here can't simply get in line because often there isn't a line. The government has a guest-worker program designed to fill seasonal jobs, but Central Valley farmers say it's too difficult to use. So they keep hiring illegal immigrants.

Yrene's mother tried several times in the late 1980s to get visas so she and her daughter could come to the United States legally, but they were denied each time. Finally, she gave up and immigrated illegally by telling a border-patrol guard they were tourists.

"We first tried to do the right thing," said Yrene, a 30-year-old packinghouse supervisor in Tulare County.

Her story is a common one. Contrary to what many people believe, most foreigners have little hope of getting a visa unless they already have close relatives in the United States or are well-educated and have specialized skills.

Pastor Michael Jordan, whose La Vina Covenant Church in Kerman is attended by many illegal immigrants, said a farmer once asked him why immigrants don't just come the legal way. The question surprised him.

"I had just assumed everybody knew how hard it is to get into this country," Jordan said. "But the poorest immigrants aren't going to be able to come here legally, so they're going to do what they have to do."

The immigration system works like this: A foreigner can come to the U.S. either by getting a temporary visa to stay for a specified period of time or a green card for legal permanent residency.

The government awards 140,000 green cards for workers each year, but almost all are reserved for skilled workers or people in special categories, such as fashion models. The small number of green cards set aside for low-skilled workers almost always go to illegal immigrants who are already working in the U.S., which means it's virtually impossible for a fieldworker in Mexico to get a green card.

The alternative is to marry a U.S. citizen or apply for one of the 480,000 green cards awarded each year to family members of legal U.S. residents. But no country is allowed more than 7% of green cards. As a consequence, ins some cases, Mexicans must wait 18 years or more for a family-sponsored green card.

A foreigner could also get lucky and win one of the 55,000 green cards awarded through a lottery each year. More than 9 million people applied for them last year.